(a) Field of the Invention
The present invention relates to novel thermosetting resin compositions useful for preparing molded articles that are heat resistant and exhibit high mechanical strength.
(b) Description of the Prior Art
Prior to the present invention, thermosetting resins having an imide structure have been extensively utilized in various industrial fields, since cured materials obtained from these resins exhibit excellent electrical insulating properties, heat resistance and dimensional stability.
However, thermosetting resins obtained by thermal polymerization of aromatic bismaleimides alone are extremely brittle and have poor flexibility although they are excellent in heat resistance. In an attempt to overcome these disadvantages, thermosetting resin compositions have been developed that contain an aromatic bismaleimide and an aromatic diamine. For example, a polyaminobismaleimide resin (Rhone-Poulenc; trade name Kelimid) comprising N,N'-4,4'-diphenylmethanebismaleimide and 4,4'-diaminodiphenylmethane is widely used in the fields of impregnating varnishes, laminated plates, molded articles and the like (Japanese Patent Laid-open Publication No. 23250/1971).
However, thermosetting resin compositions containing an aromatic bismaleimide and an aromatic diamine exhibit poor heat resistance, and unsatisfactory impact resistance and flexibility.